Health insurer WellPoint Inc posted a lower-than-expected quarterly profit on Wednesday and cut its full-year earnings forecast, citing lower enrollment and higher medical cost trends, sending its shares down 8 percent in premarket. The second-largest health insurer by market value said its medical cost trends would likely come in at the high end of its forecast, while intense competition among health plans was pressuring its enrollment. Several analysts said it was particularly discouraging that WellPoint was cutting its forecast only after backing it a couple weeks ago, when it announced its $4.5 billion acquisition of Medicaid specialist Amerigroup Inc.